Sugar alcohol collectively refers to compounds obtained by adding hydrogen atom(s) to a reducing end-group of saccharide, and generally have a chemical formula of HOCH2(CHOH)nCH2OH wherein n is an integer of 2 to 5 and is classified into tetritol, pentitol, hexitol and heptitol depending on the number of carbon atoms (4, 5, 6 and 7). Among these, hexitol containing 6 carbon atoms includes sorbitol, mannitol, iditol, and the like. In particular, sorbitol and mannitol are highly useful substances.
As a method for the preparation of an anhydrosugar alcohol using hexitol, there is known a method which includes dehydration of hexitol with an inorganic acid such as sulfuric acid or hydrochloric acid (Starch/Starke vol. 38. pp26-30). Further, dehydration of hexitol may also be carried out using cation exchange resins, zeolites, etc. Inorganic acids such as hydrochloric acid or sulfuric acid are relatively inexpensive and are capable of enabling easy preparation of anhydrosugar alcohol, but have a problem of low purification yields due to the production of large amounts of polymer by-products. On the other hand, cation exchange resins or zeolites are expensive and have problems of high recovery cost and a low conversion rate of hexitol into anhydrosugar alcohol.
Anhydrosugar alcohol is known to have a property of increasing a glass transition temperature of polymers such as polyesters. Further, it is known that anhydrosugar alcohol derivatives are beneficial for cardiac and vascular diseases, can be used in adhesives for patches, drugs such as mouthwashes, cosmetic compositions, etc., and can also be used as raw materials for environmentally-friendly plasticizers and environmentally-friendly solvents as well as raw materials for polyesters, polyurethanes, epoxy resins or the like in the chemical industry. In particular, great attention has focused on industrial applications such as polyesters, plasticizers or the like using anhydrosugar alcohol, but industrial utilization of anhydrosugar alcohol is still in-significant. This is believed to be due to limitations associated with high costs of catalysts used in dehydration reactions, low conversion rates and purification yields and the like associated with conventional methods for the preparation of an anhydrosugar alcohol.
Accordingly, there is an urgent need for a method for the preparation of an anhydrosugar alcohol which is capable of achieving high conversion rate and purification yield in conjunction with reduction of production costs.